Friday, 10 May 2019

Introduction to PostgreSQL



Installation & Running 


To start the server:

$ initdb /usr/local/pgsql/data

To start that instance:

$ postgres -D /usr/local/pgsql/data

Naming Convention


Identifiers and Key Words

SQL identifiers and key words must begin with a letter (a-z, but also letters with diacritical marks and non-Latin letters) or an underscore (_). Subsequent characters in an identifier or key word can be letters, underscores, digits (0-9), or dollar signs ($).

What is a valid PostgreSQL database name?

PostgreSQL naming conventions


Query Examples


CREATE


Create database:

CREATE DATABASE wp_dev;

CREATE DATABASE



INSERT



Insert a row into table:

INSERT INTO schema_name.table_name (col1, col2, ...) VALUES (val1, val2, ...);

Example:

my_db=# insert into my_schema.my_table (item_id, prefix, post_id) values (1, 'a1',1234);
INSERT 0 1


Does insert query has to list all columns?
No, columns that are not listed will be assigned null values.

INSERT into table without specifying Column names - this is not good practice.

SELECT 


List all table names and number of rows:

SELECT relname,n_live_tup 
FROM pg_stat_user_tables 
ORDER BY n_live_tup DESC;

Print the number of rows in a table:

select count(*) from campaign

Select all rows in a table:

SELECT * FROM my_table;

Select specific columns from a table:

SELECT col1, col2,... FROM schema.table;

Example:

my_db=# select id, item_id, prefix from my_schema.my_table;
 id | item_id | prefix 
----+---------+--------
(0 rows)


DELETE


Delete all rows from table:

DELETE FROM my_table;

PostgreSQL DELETE

Example:

my_db=# delete from my_schema.my_table;
DELETE 1



Logging


To find out the path to Postgres config file use:

jsonschema2db-test=# SHOW config_file;
            config_file             
------------------------------------
 /home/app/postgres/postgresql.conf
(1 row)

Now we can exit psql terminal and display config file:

jsonschema2db-test-# \q

bash-4.3$ cat /home/app/postgres/postgresql.conf
# -----------------------------
# PostgreSQL configuration file
# -----------------------------
#
# This file consists of lines of the form:
#
#   name = value
#
# (The "=" is optional.)  Whitespace may be used.  Comments are introduced with
# "#" anywhere on a line.  The complete list of parameter names and allowed
# values can be found in the PostgreSQL documentation.
#
# The commented-out settings shown in this file represent the default values.
# Re-commenting a setting is NOT sufficient to revert it to the default value;
# you need to reload the server.
#
# This file is read on server startup and when the server receives a SIGHUP
# signal.  If you edit the file on a running system, you have to SIGHUP the
# server for the changes to take effect, or use "pg_ctl reload".  Some
# parameters, which are marked below, require a server shutdown and restart to
# take effect.
#
# Any parameter can also be given as a command-line option to the server, e.g.,
# "postgres -c log_connections=on".  Some parameters can be changed at run time
# with the "SET" SQL command.
#
# Memory units:  kB = kilobytes        Time units:  ms  = milliseconds
#                MB = megabytes                     s   = seconds
#                GB = gigabytes                     min = minutes
#                TB = terabytes                     h   = hours
#                                                   d   = days


#------------------------------------------------------------------------------
# FILE LOCATIONS
#------------------------------------------------------------------------------

# The default values of these variables are driven from the -D command-line
# option or PGDATA environment variable, represented here as ConfigDir.

#data_directory = 'ConfigDir'           # use data in another directory
                                        # (change requires restart)
#hba_file = 'ConfigDir/pg_hba.conf'     # host-based authentication file
                                        # (change requires restart)
#ident_file = 'ConfigDir/pg_ident.conf' # ident configuration file
                                        # (change requires restart)

# If external_pid_file is not explicitly set, no extra PID file is written.
#external_pid_file = ''                 # write an extra PID file
                                        # (change requires restart)


#------------------------------------------------------------------------------
# CONNECTIONS AND AUTHENTICATION
#------------------------------------------------------------------------------

# - Connection Settings -

listen_addresses = '*'
                                        # comma-separated list of addresses;
                                        # defaults to 'localhost'; use '*' for all
                                        # (change requires restart)
#port = 5432                            # (change requires restart)
max_connections = 100                   # (change requires restart)
#superuser_reserved_connections = 3     # (change requires restart)
#unix_socket_directories = '/var/run/postgresql'        # comma-separated list of directories
                                        # (change requires restart)
#unix_socket_group = ''                 # (change requires restart)
#unix_socket_permissions = 0777         # begin with 0 to use octal notation
                                        # (change requires restart)
#bonjour = off                          # advertise server via Bonjour
                                        # (change requires restart)
#bonjour_name = ''                      # defaults to the computer name
                                        # (change requires restart)

# - Security and Authentication -

#authentication_timeout = 1min          # 1s-600s
#ssl = off                              # (change requires restart)
#ssl_ciphers = 'HIGH:MEDIUM:+3DES:!aNULL' # allowed SSL ciphers
                                        # (change requires restart)
#ssl_prefer_server_ciphers = on         # (change requires restart)
#ssl_ecdh_curve = 'prime256v1'          # (change requires restart)
#ssl_cert_file = 'server.crt'           # (change requires restart)
#ssl_key_file = 'server.key'            # (change requires restart)
#ssl_ca_file = ''                       # (change requires restart)
#ssl_crl_file = ''                      # (change requires restart)
#password_encryption = on
#db_user_namespace = off
#row_security = on

# GSSAPI using Kerberos
#krb_server_keyfile = ''
#krb_caseins_users = off

# - TCP Keepalives -
# see "man 7 tcp" for details

#tcp_keepalives_idle = 0                # TCP_KEEPIDLE, in seconds;
                                        # 0 selects the system default
#tcp_keepalives_interval = 0            # TCP_KEEPINTVL, in seconds;
                                        # 0 selects the system default
#tcp_keepalives_count = 0               # TCP_KEEPCNT;
                                        # 0 selects the system default


#------------------------------------------------------------------------------
# RESOURCE USAGE (except WAL)
#------------------------------------------------------------------------------

# - Memory -

shared_buffers = 128MB                  # min 128kB
                                        # (change requires restart)
#huge_pages = try                       # on, off, or try
                                        # (change requires restart)
#temp_buffers = 8MB                     # min 800kB
#max_prepared_transactions = 0          # zero disables the feature
                                        # (change requires restart)
# Caution: it is not advisable to set max_prepared_transactions nonzero unless
# you actively intend to use prepared transactions.
#work_mem = 4MB                         # min 64kB
#maintenance_work_mem = 64MB            # min 1MB
#replacement_sort_tuples = 150000       # limits use of replacement selection sort
#autovacuum_work_mem = -1               # min 1MB, or -1 to use maintenance_work_mem
#max_stack_depth = 2MB                  # min 100kB
dynamic_shared_memory_type = posix      # the default is the first option
                                        # supported by the operating system:
                                        #   posix
                                        #   sysv
                                        #   windows
                                        #   mmap
                                        # use none to disable dynamic shared memory

# - Disk -

#temp_file_limit = -1                   # limits per-process temp file space
                                        # in kB, or -1 for no limit

# - Kernel Resource Usage -

#max_files_per_process = 1000           # min 25
                                        # (change requires restart)
#shared_preload_libraries = ''          # (change requires restart)

# - Cost-Based Vacuum Delay -

#vacuum_cost_delay = 0                  # 0-100 milliseconds
#vacuum_cost_page_hit = 1               # 0-10000 credits
#vacuum_cost_page_miss = 10             # 0-10000 credits
#vacuum_cost_page_dirty = 20            # 0-10000 credits
#vacuum_cost_limit = 200                # 1-10000 credits

# - Background Writer -

#bgwriter_delay = 200ms                 # 10-10000ms between rounds
#bgwriter_lru_maxpages = 100            # 0-1000 max buffers written/round
#bgwriter_lru_multiplier = 2.0          # 0-10.0 multiplier on buffers scanned/round
#bgwriter_flush_after = 512kB           # measured in pages, 0 disables

# - Asynchronous Behavior -

#effective_io_concurrency = 1           # 1-1000; 0 disables prefetching
#max_worker_processes = 8               # (change requires restart)
#max_parallel_workers_per_gather = 0    # taken from max_worker_processes
#old_snapshot_threshold = -1            # 1min-60d; -1 disables; 0 is immediate
                                        # (change requires restart)
#backend_flush_after = 0                # measured in pages, 0 disables


#------------------------------------------------------------------------------
# WRITE AHEAD LOG
#------------------------------------------------------------------------------

# - Settings -

#wal_level = minimal                    # minimal, replica, or logical
                                        # (change requires restart)
#fsync = on                             # flush data to disk for crash safety
                                                # (turning this off can cause
                                                # unrecoverable data corruption)
#synchronous_commit = on                # synchronization level;
                                        # off, local, remote_write, remote_apply, or on
#wal_sync_method = fsync                # the default is the first option
                                        # supported by the operating system:
                                        #   open_datasync
                                        #   fdatasync (default on Linux)
                                        #   fsync
                                        #   fsync_writethrough
                                        #   open_sync
#full_page_writes = on                  # recover from partial page writes
#wal_compression = off                  # enable compression of full-page writes
#wal_log_hints = off                    # also do full page writes of non-critical updates
                                        # (change requires restart)
#wal_buffers = -1                       # min 32kB, -1 sets based on shared_buffers
                                        # (change requires restart)
#wal_writer_delay = 200ms               # 1-10000 milliseconds
#wal_writer_flush_after = 1MB           # measured in pages, 0 disables

#commit_delay = 0                       # range 0-100000, in microseconds
#commit_siblings = 5                    # range 1-1000

# - Checkpoints -

#checkpoint_timeout = 5min              # range 30s-1d
#max_wal_size = 1GB
#min_wal_size = 80MB
#checkpoint_completion_target = 0.5     # checkpoint target duration, 0.0 - 1.0
#checkpoint_flush_after = 256kB         # measured in pages, 0 disables
#checkpoint_warning = 30s               # 0 disables

# - Archiving -

#archive_mode = off             # enables archiving; off, on, or always
                                # (change requires restart)
#archive_command = ''           # command to use to archive a logfile segment
                                # placeholders: %p = path of file to archive
                                #               %f = file name only
                                # e.g. 'test ! -f /mnt/server/archivedir/%f && cp %p /mnt/server/archivedir/%f'
#archive_timeout = 0            # force a logfile segment switch after this
                                # number of seconds; 0 disables


#------------------------------------------------------------------------------
# REPLICATION
#------------------------------------------------------------------------------

# - Sending Server(s) -

# Set these on the master and on any standby that will send replication data.

#max_wal_senders = 0            # max number of walsender processes
                                # (change requires restart)
#wal_keep_segments = 0          # in logfile segments, 16MB each; 0 disables
#wal_sender_timeout = 60s       # in milliseconds; 0 disables

#max_replication_slots = 0      # max number of replication slots
                                # (change requires restart)
#track_commit_timestamp = off   # collect timestamp of transaction commit
                                # (change requires restart)

# - Master Server -

# These settings are ignored on a standby server.

#synchronous_standby_names = '' # standby servers that provide sync rep
                                # number of sync standbys and comma-separated list of application_name
                                # from standby(s); '*' = all
#vacuum_defer_cleanup_age = 0   # number of xacts by which cleanup is delayed

# - Standby Servers -

# These settings are ignored on a master server.

#hot_standby = off                      # "on" allows queries during recovery
                                        # (change requires restart)
#max_standby_archive_delay = 30s        # max delay before canceling queries
                                        # when reading WAL from archive;
                                        # -1 allows indefinite delay
#max_standby_streaming_delay = 30s      # max delay before canceling queries
                                        # when reading streaming WAL;
                                        # -1 allows indefinite delay
#wal_receiver_status_interval = 10s     # send replies at least this often
                                        # 0 disables
#hot_standby_feedback = off             # send info from standby to prevent
                                        # query conflicts
#wal_receiver_timeout = 60s             # time that receiver waits for
                                        # communication from master
                                        # in milliseconds; 0 disables
#wal_retrieve_retry_interval = 5s       # time to wait before retrying to
                                        # retrieve WAL after a failed attempt


#------------------------------------------------------------------------------
# QUERY TUNING
#------------------------------------------------------------------------------

# - Planner Method Configuration -

#enable_bitmapscan = on
#enable_hashagg = on
#enable_hashjoin = on
#enable_indexscan = on
#enable_indexonlyscan = on
#enable_material = on
#enable_mergejoin = on
#enable_nestloop = on
#enable_seqscan = on
#enable_sort = on
#enable_tidscan = on

# - Planner Cost Constants -

#seq_page_cost = 1.0                    # measured on an arbitrary scale
#random_page_cost = 4.0                 # same scale as above
#cpu_tuple_cost = 0.01                  # same scale as above
#cpu_index_tuple_cost = 0.005           # same scale as above
#cpu_operator_cost = 0.0025             # same scale as above
#parallel_tuple_cost = 0.1              # same scale as above
#parallel_setup_cost = 1000.0   # same scale as above
#min_parallel_relation_size = 8MB
#effective_cache_size = 4GB

# - Genetic Query Optimizer -

#geqo = on
#geqo_threshold = 12
#geqo_effort = 5                        # range 1-10
#geqo_pool_size = 0                     # selects default based on effort
#geqo_generations = 0                   # selects default based on effort
#geqo_selection_bias = 2.0              # range 1.5-2.0
#geqo_seed = 0.0                        # range 0.0-1.0

# - Other Planner Options -

#default_statistics_target = 100        # range 1-10000
#constraint_exclusion = partition       # on, off, or partition
#cursor_tuple_fraction = 0.1            # range 0.0-1.0
#from_collapse_limit = 8
#join_collapse_limit = 8                # 1 disables collapsing of explicit
                                        # JOIN clauses
#force_parallel_mode = off


#------------------------------------------------------------------------------
# ERROR REPORTING AND LOGGING
#------------------------------------------------------------------------------

# - Where to Log -

#log_destination = 'stderr'             # Valid values are combinations of
                                        # stderr, csvlog, syslog, and eventlog,
                                        # depending on platform.  csvlog
                                        # requires logging_collector to be on.

# This is used when logging to stderr:
#logging_collector = off                # Enable capturing of stderr and csvlog
                                        # into log files. Required to be on for
                                        # csvlogs.
                                        # (change requires restart)

# These are only used if logging_collector is on:
#log_directory = 'pg_log'               # directory where log files are written,
                                        # can be absolute or relative to PGDATA
#log_filename = 'postgresql-%Y-%m-%d_%H%M%S.log'        # log file name pattern,
                                        # can include strftime() escapes
#log_file_mode = 0600                   # creation mode for log files,
                                        # begin with 0 to use octal notation
#log_truncate_on_rotation = off         # If on, an existing log file with the
                                        # same name as the new log file will be
                                        # truncated rather than appended to.
                                        # But such truncation only occurs on
                                        # time-driven rotation, not on restarts
                                        # or size-driven rotation.  Default is
                                        # off, meaning append to existing files
                                        # in all cases.
#log_rotation_age = 1d                  # Automatic rotation of logfiles will
                                        # happen after that time.  0 disables.
#log_rotation_size = 10MB               # Automatic rotation of logfiles will
                                        # happen after that much log output.
                                        # 0 disables.

# These are relevant when logging to syslog:
#syslog_facility = 'LOCAL0'
#syslog_ident = 'postgres'
#syslog_sequence_numbers = on
#syslog_split_messages = on

# This is only relevant when logging to eventlog (win32):
#event_source = 'PostgreSQL'

# - When to Log -

#client_min_messages = notice           # values in order of decreasing detail:
                                        #   debug5
                                        #   debug4
                                        #   debug3
                                        #   debug2
                                        #   debug1
                                        #   log
                                        #   notice
                                        #   warning
                                        #   error

#log_min_messages = warning             # values in order of decreasing detail:
                                        #   debug5
                                        #   debug4
                                        #   debug3
                                        #   debug2
                                        #   debug1
                                        #   info
                                        #   notice
                                        #   warning
                                        #   error
                                        #   log
                                        #   fatal
                                        #   panic

#log_min_error_statement = error        # values in order of decreasing detail:
                                        #   debug5
                                        #   debug4
                                        #   debug3
                                        #   debug2
                                        #   debug1
                                        #   info
                                        #   notice
                                        #   warning
                                        #   error
                                        #   log
                                        #   fatal
                                        #   panic (effectively off)

#log_min_duration_statement = -1        # -1 is disabled, 0 logs all statements
                                        # and their durations, > 0 logs only
                                        # statements running at least this number
                                        # of milliseconds


# - What to Log -

#debug_print_parse = off
#debug_print_rewritten = off
#debug_print_plan = off
#debug_pretty_print = on
#log_checkpoints = off
#log_connections = off
#log_disconnections = off
#log_duration = off
#log_error_verbosity = default          # terse, default, or verbose messages
#log_hostname = off
#log_line_prefix = ''                   # special values:
                                        #   %a = application name
                                        #   %u = user name
                                        #   %d = database name
                                        #   %r = remote host and port
                                        #   %h = remote host
                                        #   %p = process ID
                                        #   %t = timestamp without milliseconds
                                        #   %m = timestamp with milliseconds
                                        #   %n = timestamp with milliseconds (as a Unix epoch)
                                        #   %i = command tag
                                        #   %e = SQL state
                                        #   %c = session ID
                                        #   %l = session line number
                                        #   %s = session start timestamp
                                        #   %v = virtual transaction ID
                                        #   %x = transaction ID (0 if none)
                                        #   %q = stop here in non-session
                                        #        processes
                                        #   %% = '%'
                                        # e.g. '<%u%%%d> '
#log_lock_waits = off                   # log lock waits >= deadlock_timeout
#log_statement = 'none'                 # none, ddl, mod, all
#log_replication_commands = off
#log_temp_files = -1                    # log temporary files equal or larger
                                        # than the specified size in kilobytes;
                                        # -1 disables, 0 logs all temp files
log_timezone = 'UTC'


# - Process Title -

#cluster_name = ''                      # added to process titles if nonempty
                                        # (change requires restart)
#update_process_title = on


#------------------------------------------------------------------------------
# RUNTIME STATISTICS
#------------------------------------------------------------------------------

# - Query/Index Statistics Collector -

#track_activities = on
#track_counts = on
#track_io_timing = off
#track_functions = none                 # none, pl, all
#track_activity_query_size = 1024       # (change requires restart)
#stats_temp_directory = 'pg_stat_tmp'


# - Statistics Monitoring -

#log_parser_stats = off
#log_planner_stats = off
#log_executor_stats = off
#log_statement_stats = off


#------------------------------------------------------------------------------
# AUTOVACUUM PARAMETERS
#------------------------------------------------------------------------------

#autovacuum = on                        # Enable autovacuum subprocess?  'on'
                                        # requires track_counts to also be on.
#log_autovacuum_min_duration = -1       # -1 disables, 0 logs all actions and
                                        # their durations, > 0 logs only
                                        # actions running at least this number
                                        # of milliseconds.
#autovacuum_max_workers = 3             # max number of autovacuum subprocesses
                                        # (change requires restart)
#autovacuum_naptime = 1min              # time between autovacuum runs
#autovacuum_vacuum_threshold = 50       # min number of row updates before
                                        # vacuum
#autovacuum_analyze_threshold = 50      # min number of row updates before
                                        # analyze
#autovacuum_vacuum_scale_factor = 0.2   # fraction of table size before vacuum
#autovacuum_analyze_scale_factor = 0.1  # fraction of table size before analyze
#autovacuum_freeze_max_age = 200000000  # maximum XID age before forced vacuum
                                        # (change requires restart)
#autovacuum_multixact_freeze_max_age = 400000000        # maximum multixact age
                                        # before forced vacuum
                                        # (change requires restart)
#autovacuum_vacuum_cost_delay = 20ms    # default vacuum cost delay for
                                        # autovacuum, in milliseconds;
                                        # -1 means use vacuum_cost_delay
#autovacuum_vacuum_cost_limit = -1      # default vacuum cost limit for
                                        # autovacuum, -1 means use
                                        # vacuum_cost_limit


#------------------------------------------------------------------------------
# CLIENT CONNECTION DEFAULTS
#------------------------------------------------------------------------------

# - Statement Behavior -

#search_path = '"$user", public'        # schema names
#default_tablespace = ''                # a tablespace name, '' uses the default
#temp_tablespaces = ''                  # a list of tablespace names, '' uses
                                        # only default tablespace
#check_function_bodies = on
#default_transaction_isolation = 'read committed'
#default_transaction_read_only = off
#default_transaction_deferrable = off
#session_replication_role = 'origin'
#statement_timeout = 0                  # in milliseconds, 0 is disabled
#lock_timeout = 0                       # in milliseconds, 0 is disabled
#idle_in_transaction_session_timeout = 0                # in milliseconds, 0 is disabled
#vacuum_freeze_min_age = 50000000
#vacuum_freeze_table_age = 150000000
#vacuum_multixact_freeze_min_age = 5000000
#vacuum_multixact_freeze_table_age = 150000000
#bytea_output = 'hex'                   # hex, escape
#xmlbinary = 'base64'
#xmloption = 'content'
#gin_fuzzy_search_limit = 0
#gin_pending_list_limit = 4MB

# - Locale and Formatting -

datestyle = 'iso, mdy'
#intervalstyle = 'postgres'
timezone = 'UTC'
#timezone_abbreviations = 'Default'     # Select the set of available time zone
                                        # abbreviations.  Currently, there are
                                        #   Default
                                        #   Australia (historical usage)
                                        #   India
                                        # You can create your own file in
                                        # share/timezonesets/.
#extra_float_digits = 0                 # min -15, max 3
#client_encoding = sql_ascii            # actually, defaults to database
                                        # encoding

# These settings are initialized by initdb, but they can be changed.
lc_messages = 'en_US.utf-8'                     # locale for system error message
                                        # strings
lc_monetary = 'en_US.utf-8'                     # locale for monetary formatting
lc_numeric = 'en_US.utf-8'                      # locale for number formatting
lc_time = 'en_US.utf-8'                         # locale for time formatting

# default configuration for text search
default_text_search_config = 'pg_catalog.english'

# - Other Defaults -

#dynamic_library_path = '$libdir'
#local_preload_libraries = ''
#session_preload_libraries = ''


#------------------------------------------------------------------------------
# LOCK MANAGEMENT
#------------------------------------------------------------------------------

#deadlock_timeout = 1s
#max_locks_per_transaction = 64         # min 10
                                        # (change requires restart)
#max_pred_locks_per_transaction = 64    # min 10
                                        # (change requires restart)


#------------------------------------------------------------------------------
# VERSION/PLATFORM COMPATIBILITY
#------------------------------------------------------------------------------

# - Previous PostgreSQL Versions -

#array_nulls = on
#backslash_quote = safe_encoding        # on, off, or safe_encoding
#default_with_oids = off
#escape_string_warning = on
#lo_compat_privileges = off
#operator_precedence_warning = off
#quote_all_identifiers = off
#sql_inheritance = on
#standard_conforming_strings = on
#synchronize_seqscans = on

# - Other Platforms and Clients -

#transform_null_equals = off


#------------------------------------------------------------------------------
# ERROR HANDLING
#------------------------------------------------------------------------------

#exit_on_error = off                    # terminate session on any error?
#restart_after_crash = on               # reinitialize after backend crash?


#------------------------------------------------------------------------------
# CONFIG FILE INCLUDES
#------------------------------------------------------------------------------

# These options allow settings to be loaded from files other than the
# default postgresql.conf.

#include_dir = 'conf.d'                 # include files ending in '.conf' from
                                        # directory 'conf.d'
#include_if_exists = 'exists.conf'      # include file only if it exists
#include = 'special.conf'               # include file


#------------------------------------------------------------------------------
# CUSTOMIZED OPTIONS
#------------------------------------------------------------------------------

# Add settings for extensions here


To debug errors in Postgres client apps it is useful to check Postgres logs:

$ tail -10 /usr/local/var/log/postgres.log



psql


$ psql --help
psql is the PostgreSQL interactive terminal.

Usage:
  psql [OPTION]... [DBNAME [USERNAME]]

General options:
  -c, --command=COMMAND    run only single command (SQL or internal) and exit

  -d, --dbname=DBNAME      database name to connect to (default: "dbuser") // this is the name returned by whoami command in shell

  -f, --file=FILENAME      execute commands from file, then exit

  -l, --list               list available databases, then exit

  -v, --set=, --variable=NAME=VALUE
                           set psql variable NAME to VALUE
                           (e.g., -v ON_ERROR_STOP=1)
  -V, --version            output version information, then exit
  -X, --no-psqlrc          do not read startup file (~/.psqlrc)
  -1 ("one"), --single-transaction
                           execute as a single transaction (if non-interactive)
  -?, --help[=options]     show this help, then exit
      --help=commands      list backslash commands, then exit
      --help=variables     list special variables, then exit

Input and output options:
  -a, --echo-all           echo all input from script
  -b, --echo-errors        echo failed commands
  -e, --echo-queries       echo commands sent to server

  -E, --echo-hidden        display queries that internal commands generate // If you start psql with the -E flag, it will display the real query when you use a meta-command.

  -L, --log-file=FILENAME  send session log to file
  -n, --no-readline        disable enhanced command line editing (readline)
  -o, --output=FILENAME    send query results to file (or |pipe)
  -q, --quiet              run quietly (no messages, only query output)
  -s, --single-step        single-step mode (confirm each query)
  -S, --single-line        single-line mode (end of line terminates SQL command)

Output format options:
  -A, --no-align           unaligned table output mode
  -F, --field-separator=STRING
                           field separator for unaligned output (default: "|")
  -H, --html               HTML table output mode
  -P, --pset=VAR[=ARG]     set printing option VAR to ARG (see \pset command)
  -R, --record-separator=STRING
                           record separator for unaligned output (default: newline)
  -t, --tuples-only        print rows only
  -T, --table-attr=TEXT    set HTML table tag attributes (e.g., width, border)
  -x, --expanded           turn on expanded table output
  -z, --field-separator-zero
                           set field separator for unaligned output to zero byte
  -0, --record-separator-zero
                           set record separator for unaligned output to zero byte

Connection options:
  -h, --host=HOSTNAME      database server host or socket directory (default: "local socket")
  -p, --port=PORT          database server port (default: "5432")

  -U, --username=USERNAME  database user name (default: "dbuser")

  -w, --no-password        never prompt for password
  -W, --password           force password prompt (should happen automatically)

For more information, type "\?" (for internal commands) or "\help" (for SQL
commands) from within psql, or consult the psql section in the PostgreSQL
documentation.

Report bugs to <pgsql-bugs@postgresql.org>.




$ psql
psql: FATAL:  database "dbuser" does not exist

psql takes the name of the process owner as the name of the database that it's supposed to connect. As database dbuser does not exist, psql prints that error above.


$ psql --version
psql (PostgreSQL) 11.2

To list all regular databases:

psql -l
                                   List of databases
        Name        | Owner  | Encoding |   Collate   |    Ctype    | Access privileges 
--------------------+--------+----------+-------------+-------------+-------------------
 jsonschema2db-test | dbuser | UTF8     | en_US.utf-8 | en_US.utf-8 | 
 postgres           | dbuser | UTF8     | en_US.utf-8 | en_US.utf-8 | 
 template0          | dbuser | UTF8     | en_US.utf-8 | en_US.utf-8 | =c/dbuser        +
                    |        |          |             |             | dbuser=CTc/dbuser
 template1          | dbuser | UTF8     | en_US.utf-8 | en_US.utf-8 | =c/dbuser        +
                    |        |          |             |             | dbuser=CTc/dbuser
(4 rows)

Now we can connect to some database:

$ psql postgres
psql (11.2)
Type "help" for help.
postgres=# 

To disconnect from it and connect to some other database use

\connect db_name

or

\c db_name


We can now create a new database:

postgres=# create database testdb;
CREATE DATABASE

To list databases after getting connected to some DB, just issue commands:

postgres=# \l
                                   List of databases
        Name        | Owner  | Encoding |   Collate   |    Ctype    | Access privileges 
--------------------+--------+----------+-------------+-------------+-------------------
 jsonschema2db-test | dbuser | UTF8     | en_US.utf-8 | en_US.utf-8 | 
 postgres           | dbuser | UTF8     | en_US.utf-8 | en_US.utf-8 | 
 template0          | dbuser | UTF8     | en_US.utf-8 | en_US.utf-8 | =c/dbuser        +
                    |        |          |             |             | dbuser=CTc/dbuser
 template1          | dbuser | UTF8     | en_US.utf-8 | en_US.utf-8 | =c/dbuser        +
                    |        |          |             |             | dbuser=CTc/dbuser
 testdb             | dbuser | UTF8     | en_US.utf-8 | en_US.utf-8 | 
(5 rows)

To see extended info on existing databases:

testdb=# \l+
                                                                     List of databases
        Name        | Owner  | Encoding |   Collate   |    Ctype    | Access privileges |  Size   | Tablespace |                Description                 
--------------------+--------+----------+-------------+-------------+-------------------+---------+------------+--------------------------------------------
 jsonschema2db-test | dbuser | UTF8     | en_US.utf-8 | en_US.utf-8 |                   | 7763 kB | pg_default | 
 postgres           | dbuser | UTF8     | en_US.utf-8 | en_US.utf-8 |                   | 7699 kB | pg_default | default administrative connection database
 template0          | dbuser | UTF8     | en_US.utf-8 | en_US.utf-8 | =c/dbuser        +| 7561 kB | pg_default | unmodifiable empty database
                    |        |          |             |             | dbuser=CTc/dbuser |         |            | 
 template1          | dbuser | UTF8     | en_US.utf-8 | en_US.utf-8 | =c/dbuser        +| 7561 kB | pg_default | default template for new databases
                    |        |          |             |             | dbuser=CTc/dbuser |         |            | 
 testdb             | dbuser | UTF8     | en_US.utf-8 | en_US.utf-8 |                   | 7699 kB | pg_default | 
(5 rows)


Schemas are namespaces: you may have different tables with same name in different namespaces.

To list all tables for public schema use

\dt

To list all tables in all schemas:

\dt *.* 

To list tables in a particular schema use:

\dt schema_name.*

List tables in a PostgreSQL schema


$ psql jsonschema2db-test
psql (11.2)
Type "help" for help.

jsonschema2db-test=#


sonschema2db-test-# \du
                                   List of roles
 Role name |                         Attributes                         | Member of
-----------+------------------------------------------------------------+-----------
 dbuser    | Superuser, Create role, Create DB, Replication, Bypass RLS | {}


To list all constrains in some table (with psql):

my_db=# \d+ schema_name.table_name;

Example:


my_db=# \d+ my_schema.my_table;
                                                                              Table "my_schema.my_table"
                      Column                       |       Type       | Collation | Nullable |                      Default                      | Storage  | Stats target | Description 
---------------------------------------------------+------------------+-----------+----------+---------------------------------------------------+----------+--------------+-------------
 id                                                | integer          |           | not null | nextval('block_filterlist.root_id_seq'::regclass) | plain    |              | 
 item_id                                           | bigint           |           | not null |                                                   | plain    |              | 
 prefix                                            | text             |           | not null |                                                   | extended |              | 
 attachments                                       | text             |           |          |                                                   | 

...

extended |              | 
 type                                              | text             |           |          |                                                   | extended |              | 
 url                                               | text             |           |          |                                                   | extended |              | 
Indexes:
    "root_id_key" UNIQUE CONSTRAINT, btree (id)
    "root_item_id_prefix_key" UNIQUE CONSTRAINT, btree (item_id, prefix)

If you try to insert two rows with the same value for item_id Postgres will issue an error:

ERROR:  duplicate key value violates unique constraint "root_item_id_prefix_key"
DETAIL:  Key (item_id, prefix)=(0, 0) already exists.
STATEMENT:  insert into my_schema.my_table (item_id, post_id, prefix) values(0, 1234, 0) returning id


PostgreSQL Docker Image


If Dockerfile contains the command which starts the Postgres server:

CMD pg_ctl -w start


...then, when running docker image we get:

$ docker run jsonschema2db-demo
pg_ctl: cannot be run as root
Please log in (using, e.g., "su") as the (unprivileged) user that will
own the server process.

This is because 

“By default docker containers run as root. (…) As docker matures, more secure default options may become available. For now, requiring root is dangerous for others and may not be available in all environments. Your image should use the USER instruction to specify a non-root user for containers to run as”. (From Guidance for Docker Image Authors)

Quick fix:

RUN adduser --disabled-password dbuser
USER dbuser
CMD pg_ctl -w start

---

Running 

CMD pg_ctl -w start

might output the following error:

pg_ctl: directory "/var/lib/postgresql/data" is not a database cluster directory



You're getting this error because there is no database cluster created inside the postgres docker image when you're attempting to run the pg_ctl start command.

The database cluster is created when you run a docker container based on the image, as the initdb binary is called as part of the docker-entrypoint.sh script that is set as the ENTRYPOINT for the postgres container.

Fix:

RUN initdb

---

Execution of

RUN initdb

might output the following eror:

initdb: could not change permissions of directory "/var/lib/postgresql/data": Operation not permitted
The files belonging to this database system will be owned by user "dbuser".
This user must also own the server process.

The database cluster will be initialized with locale "en_US.utf8".
The default database encoding has accordingly been set to "UTF8".
The default text search configuration will be set to "english".

Data page checksums are disabled.

fixing permissions on existing directory /var/lib/postgresql/data ... The command '/bin/sh -c initdb' returned a non-zero code: 1


From Running PostgreSQL using Docker Compose:

Docker volumes are the recommended way to persist data. These are file systems managed by the Docker daemon and more often than not you are expected to create one and mount it inside your container when you launch it. The Postgres official image, however, comes with a VOLUME predefined in its image description.

This means that when you run a PostgreSQL image as a container, it creates a volume for itself and stores data in there.

Let's inspect the docker container mypostgres to see volumes mounted inside the database container:

$ docker inspect mypostgres

            "Env": [
                "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
                "LANG=en_US.utf8",
                "PG_MAJOR=11",
                "PG_VERSION=11.2",
                "PG_SHA256=2676b9ce09c21978032070b6794696e0aa5a476e3d21d60afc036dc0a9c09405",
                "PGDATA=/var/lib/postgresql/data",
                ...
            ],
...
            "Volumes": {
                "/var/lib/postgresql/data": {}
            },
            "Entrypoint": [
                "docker-entrypoint.sh"
            ],

From Postgres docs:

Traditionally, the configuration and data files used by a database cluster are stored together within the cluster's data directory, commonly referred to as PGDATA (after the name of the environment variable that can be used to define it). A common location for PGDATA is /var/lib/pgsql/data.

The cause of the error above is that root is the owner of /var/lib/postgresql/data and initdb has to be run as non-root so it can't access it to initialize DB.

Fix:

Set some other directory, owned by non-root user (or the same user that runs initdb), as PGDATA value:

USER dbuser
ENV PGDATA /home/dbuser/pgdata
RUN initdb

---

Executing

RUN initdb

...might output the following:


 ---> Running in 7175f5b08c6b
The files belonging to this database system will be owned by user "dbuser".
This user must also own the server process.

The database cluster will be initialized with locale "en_US.utf8".

The default database encoding has accordingly been set to "UTF8".
The default text search configuration will be set to "english".

Data page checksums are disabled.


creating directory /home/dbuser/pgdata ... ok

creating subdirectories ... ok
selecting default max_connections ... 100
selecting default shared_buffers ... 128MB
selecting dynamic shared memory implementation ... posix
creating configuration files ... ok
running bootstrap script ... ok
performing post-bootstrap initialization ... sh: locale: not found
2019-04-25 11:51:46.011 UTC [10] WARNING:  no usable system locales were found
ok
syncing data to disk ... ok

Success. You can now start the database server using:


    pg_ctl -D /home/dbuser/pgdata -l logfile start


To fix this, define and set LC_ALL environment variable:

USER dbuser
ENV PGDATA /home/dbuser/pgdata
ENV LC_ALL=en_US.utf-8
RUN initdb

---

When executing

CMD pg_ctl -w start && createdb jsonschema2db-test && python3 main.py

Postgres container will exit as soon as all commands are executed. If we want to make this container running until we stop it, we can add launching bash:

CMD pg_ctl -w start && createdb jsonschema2db-test && python3 main.py && /bin/bash

and run this container in the background:

$ docker run -dt mydb

Use docker ps to verify this.

----

How to query Postgres running in a container


First open a bash in it:

$ docker exec -it c5158bf4cb0c bash

Then run in bash psql terminal:

$ psql

Example (DB_USER=postgres, DB_PASSWORD=postgres; bash user is root):

$ docker exec -it my_app_db_1 bash

root@4c0cce87ba63:/# psql -l
psql: FATAL:  role "root" does not exist

root@4c0cce87ba63:/# psql
psql: FATAL:  role "root" does not exist

root@4c0cce87ba63:/# psql -l user=postgres
                                 List of databases
   Name    |  Owner   | Encoding |  Collate   |   Ctype    |   Access privileges   
-----------+----------+----------+------------+------------+-----------------------
 postgres  | postgres | UTF8     | en_US.utf8 | en_US.utf8 | 
 template0 | postgres | UTF8     | en_US.utf8 | en_US.utf8 | =c/postgres          +
           |          |          |            |            | postgres=CTc/postgres
 template1 | postgres | UTF8     | en_US.utf8 | en_US.utf8 | =c/postgres          +
           |          |          |            |            | postgres=CTc/postgres
 my_app_dev    | postgres | UTF8     | en_US.utf8 | en_US.utf8 | 
(4 rows)

root@4c0cce87ba63:/# psql my_app_dev
psql: FATAL:  role "root" does not exist

root@4c0cce87ba63:/# psql wp_dev postgres
psql (11.3 (Debian 11.3-1.pgdg90+1))
Type "help" for help.

my_app_dev=# \dn
       List of schemas
       Name       |  Owner   
------------------+----------
my_schema | postgres
 public           | postgres
 test             | postgres
(3 rows)

my_app_dev=# select * from my_schema.root;
 id | item_id | prefix | attachments |....status | tags | title | title_plain | type | url 
----+---------+--------+-------------+--------------------+-------------------+-----------+------------------+-------
(0 rows)

my_app_dev=# 

---

How to execute some SQL queries (e.g. create a new database) upon launching Postgres in Docker container?


We usually want to build the database structure so we can have init.sql (and other scripts) which contains all the CREATE TABLE statements. This file has to be mapped into docker-entrypoint-initdb.d where Postgres picks it up and sql scripts are executed.

The following example shows how to create database on the Postgres launch. Note that init scripts will run only on the first run of the database initailization.

Data directory must be empty when you start the container (the named volume from your compose). The scripts are only run on first database creation; if you compose down/stop/kill and then up they will not run anything new. [source]

init.sql:

CREATE DATABASE my_db;

docker-compose.yml

services:
  db:
    image: postgres:latest
    volumes:
      - ./db/init.sql:/docker-entrypoint-initdb.d/init.sql

docker-compose up output:

2019-05-10 09:06:32.033 UTC [42] LOG:  database system is ready to accept connections
db_1         |  done
db_1         | server started
db_1         | /usr/local/bin/docker-entrypoint.sh: running /docker-entrypoint-initdb.d/init.sql
db_1         | CREATE DATABASE



TBC...


https://dba.stackexchange.com/questions/58312/how-to-get-the-name-of-the-current-database-from-within-postgresql

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